Arxiv Selection April 2019

April 1-April 7 Biao Huang, April 8-April 14 Sayan Choudhury, April 15-April 21 Zehan Li, April 22- April 28 Jiansong Pan

Apr 26

arXiv:1904.10995 [pdf, other]

Momentum-space atom correlations in a Mott insulator

Cécile Carcy, Hugo Cayla, Antoine Tenart, Alain Aspect, Marco Mancini, David Clément

Comments: 13 pages, 10 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)

We report on the investigation of the three-dimensional single-atom-resolved distributions of bosonic Mott insulators in momentum-space. Firstly, we measure the two-body and three-body correlations deep in the Mott regime, finding a perfectly contrasted bunching whose periodicity reproduces the reciprocal lattice. In addition, we show that the two-body correlation length is inversely proportional to the in-trap size of the Mott state with a pre-factor in agreement with the prediction for an incoherent state occupying a uniformly filled lattice. Our findings indicate that the momentum-space correlations of a Mott insulator at small tunnelling is that of a many-body ground-state with Gaussian statistics. Secondly, in the Mott insulating regime with increasing tunnelling, we extract the spectral weight of the quasi-particles from the momentum density profiles. On approaching the transition towards a superfluid, the momentum spread of the spectral weight is found to decrease as a result of the increased mobility of the quasi-particles in the lattice. While the shapes of the observed spectral weight agree with the ones predicted by perturbative many-body calculations, the fitted mobilities are larger than the theoretical ones. This discrepancy is similar to that previously reported on the time-of-flight visibility.

Apr 25

arXiv:1904.10868 [pdf, ps, other]

Quantum density anomaly in optically trapped ultracold gases

Eduardo O. Rizzatti, Marco Aurelio A. Barbosa, Marcia C. Barbosa

Subjects: Quantum Gases (cond-mat.quant-gas)

We show that the Bose-Hubbard Model exhibits an increase in density with temperature at fixed pressure in the regular fluid regime and in the superfluid phase. The anomaly at the Bose-Einstein condensate is the first density anomaly observed in a quantum state. We propose that the mechanism underlying both the normal phase and the superfluid phase anomalies is related to zero point entropies and ground state phase transitions. A connection with the typical experimental scales and setups is also addressed. This key finding opens a new pathway for theoretical and experimental studies of water-like anomalies in the area of ultracold quantum gases.

arXiv:1904.10553 [pdf, other]

Quantum Adiabatic Doping with Incommensurate Optical Lattices

Jian Lin, Jue Nan, Yuchen Luo, Xing-Can Yao, Xiaopeng Li

Comments: 6 pages, 3 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph

Quantum simulations of Fermi-Hubbard models have been attracting considerable efforts in the optical lattice research, with the ultracold anti-ferromagnetic atomic phase reached at half filling in recent years. An unresolved issue is to dope the system while maintaining the low thermal entropy. Here we propose to achieve the low temperature phase of the doped Fermi-Hubbard model using incommensurate optical lattices through adiabatic quantum evolution. In this theoretical proposal, we find that one major problem about the adiabatic doping that shows up is atomic localization in the incommensurate lattice, potentially causing exponential slowing down of the adiabatic procedure. We study both one- and two-dimensional incommensurate optical lattices, and find that the localization prevents efficient adiabatic doping in the strong lattice regime for both cases. With density matrix renormalization group calculation, we further show that the slowing down problem in one dimension can be circumvented by considering interaction induced many-body delocalization, which is experimentally feasible using Feshbach resonance techniques. This protocol is expected to be efficient as well in two dimensions where the localization phenomenon is less stable.

Apr 24

arXiv:1904.10349 [pdf, other]

Quantum correlations in dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equation

Fabian Böttcher, Matthias Wenzel, Jan-Niklas Schmidt, Mingyang Guo, Tim Langen, Igor Ferrier-Barbut, Tilman Pfau, Raúl Bombín, Joan Sánchez-Baena, Jordi Boronat, Ferran Mazzanti

Subjects: Quantum Gases (cond-mat.quant-gas)

Dipolar quantum droplets are exotic quantum objects that are self-bound due to the subtle balance of attraction, repulsion and quantum correlations. Here we present a systematic study of the critical atom number of these self-bound droplets, comparing the experimental results with extended mean-feld Gross-Pitaevskii equation (eGPE) and quantum Monte-Carlo simulations of the dilute system. The respective theoretical predictions differ and we show that the experiment supports the quantum Monte-Carlo results. This calls into question the validity of the current theoretical state-of-the-art description of quantum droplets within the eGPE framework and shows that our system can serve as a sensitive testing ground for many-body theories.

arXiv:1904.10050 [pdf]

Metastability of quantum droplet clusters

Yaroslav V. Kartashov, Boris A. Malomed, Lluis Torner

Comments: 5 pages, 6 figures, to appear in Physical Review Letters

Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Pattern Formation and Solitons (nlin.PS)

We show that metastable ring-shaped clusters can be constructed from two-dimensional quantum droplets in systems described by the Gross-Pitaevskii equations augmented with Lee-Huang-Yang quantum corrections. The clusters exhibit dynamical behaviours ranging from contraction to rotation with simultaneous periodic pulsations, or expansion, depending on the initial radius of the necklace pattern and phase shift between adjacent quantum droplets. We show that, using an energy-minimization analysis, one can predict equilibrium values of the cluster radius that correspond to rotation without radial pulsations. In such a regime, the clusters evolve as metastable states, withstanding abrupt variations in the underlying scattering lengths and keeping their azimuthal symmetry in the course of evolution, even in the presence of considerable perturbations.

Apr 22

arXiv:1904.09118 [pdf, other]

Topological supersolids with tunable chern numbers of a dipolar Fermi gas in a three-dimensional anisotropic optical lattice

Shuai Li, Biao Dong, Hongrong Li, Fuli Li, Bo Liu

Comments: 7 pages, 4 figures, including Supplementary Material

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

Supersolids are among the most desirable unconventional many-body quantum states, which are linked to the fundamental issue of the coexistence of crystalline long-range order and off-diagonal long-range order (superfluidity). The recent experimental breakthrough in implementation of tuning the dipole-dipole interaction with a rotating magnetic field in quantum gases [Phys. Rev. Lett. 120, 230401 (2018)] opens up a new thrust towards discovering new types of supersolids, which have no prior analogs in previous studies. Here we report that various fantastic topological supersolids emerge in a single-component dipolar Fermi gas trapped in an anisotropic 3D optical lattice with an effective dipolar interaction engineered by a rotating external field. Through simply adjusting the average filling of our proposed lattice system, these supersolids demonstrate novel features with highly tunable chern numbers. The system undergoes phase transitions between a p-wave superfluid and different topological supersolids when increasing the dipolar interaction, whose experimental signatures include the highly number-adjustable chiral edge modes as well as Majorana Fermions.

Apr 19

arXiv:1904.08700 [pdf, ps, other]

Correlation functions of one-dimensional polar-molecules on optical lattices

Theja N. De Silva

Comments: Nine pages with two figures

Subjects: Quantum Gases (cond-mat.quant-gas)

We combine a slave-spin approach with a mean-field theory to develop an approximate theoretical scheme to study the charge (particle), spin, and, pairing correlation functions of fermionic polar molecules. We model the polar molecules subjected to a one-dimensional periodic optical lattice potential using a generalized t − J model, where the long range part of the interaction is included through the exchange interaction parameter. For this model, we derive a set of self-consistent equations for the correlation functions, and evaluate them numerically for specific cases. We find that the pairing correlations are related to spin correlations through the doping level and the slavespin correlations. Further, our calculations indicates that the long range character of the interaction can be probed through these correlation functions. In the absence of exact solutions for the onedimensional t − J model, our approximate theoretical treatment can be treated as a useful tool to study one dimensional long range correlated fermions.

Apr 18

arXiv:1904.08388 [pdf, other]

Dynamical spin-orbit coupling of a quantum gas

Ronen M. Kroeze, Yudan Guo, Benjamin L. Lev

Comments: 4 pages, 4 figures; 2 pages of supplemental material

Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We realize the dynamical 1D spin-orbit-coupling (SOC) of a Bose-Einstein condensate confined within an optical cavity. The SOC emerges through spin-correlated momentum impulses delivered to the atoms via Raman transitions. These are effected by classical pump fields acting in concert with the quantum dynamical cavity field. Above a critical pump power, the Raman coupling emerges as the atoms superradiantly populate the cavity mode with photons. Concomitantly, these photons cause a back-action onto the atoms, forcing them to order their spin-spatial state. This SOC-inducing superradiant Dicke phase transition results in a spinor-helix polariton condensate. We observe emergent SOC through spin-resolved atomic momentum imaging. Dynamical SOC in quantum gas cavity QED, and the extension to dynamical gauge fields, may enable the creation of Meissner-like effects, topological superfluids, and exotic quantum Hall states in coupled light-matter systems.

Apr 17

arXiv:1904.07649 (cross-list from cond-mat.dis-nn) [pdf, ps, other]

Dipolar Bose gas with three-body interactions in weak disorder

Redaouia Keltoum, Abdelaali Boudjemaa

Comments: 6 pages, 3 figures

Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas)

We study effects of weak disorder with Gaussian correlation function on a dipolar Bose gas with three-body interactions using the Hartree-Fock-Bogoliubov theory. Corrections due to quantum, thermal and disorder fluctuations to the condensate depletion, the one-body density correlation function as well as to the equation of state and the ground state energy are properly calculated. We show that the intriguing interplay of the disorder, dipole-dipole interactions and three-body interactions plays a fundamental role in the physics of the system. Interestingly, we find that the three-body interactions release atoms localized in the respective minima of the random potential.

Apr 16

arXiv:1904.07009 [pdf, other]

Exactly solvable model of two interacting Rydberg-dressed atoms confined in a two-dimensional harmonic trap

Przemysław Kościk, Tomas Sowiński

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Exactly solvable model of two Rydberg-dressed atoms moving in a quasi-two-dimensional harmonic trap is introduced and its properties are investigated. Depending on the strength of inter-particle interactions and the critical range of the potential, the two-particle eigenstates are classified with respect to the excitations of the center-of-mass motion, relative angular momentum, and relative distance variable. Having these solutions in hand, we discuss inter-particle correlations as functions of interaction parameters. We also present a straightforward prescription of how to generalize obtained solutions to higher dimensions.

Apr 15

arXiv:1904.06208 [pdf, other]

Quench induced vortex-bright-soliton formation in binary Bose-Einstein condensates

K. Mukherjee, S. I. Mistakidis, P. G. Kevrekidis, P. Schmelcher

Comments: 16 pages, 10 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We unravel the spontaneous generation of vortex-bright-soliton structures in binary Bose-Einstein condensates confined in a two-dimensional harmonic trap where one of the two species has been segmented into two parts by a potential barrier. To trigger the dynamics the potential barrier is suddenly removed and subsequently the segments perform a counterflow dynamics. We consider a relative phase difference of π between the segments, while a singly quantized or no vortex is imprinted at the center of the other species. The number of vortex structures developed within the segmented species after the merging of its segments is found to depend on the potential presence of the initial vortex on the other species. In particular, a π phase difference in the segmented species and a vortex in the other species result in a single vortex-bright-soliton structure. However, when the non-segmented species does not contain a vortex the counterflow dynamics of the segmented species gives rise to a vortex dipole in it accompanied by two bright solitary waves arising in the non-segmented species. Inspecting the dynamics of the angular momentum we show that it can be transferred from one species to the other, and its transfer rate can be tuned by the strength of the interspecies interactions.

Apr 3

arXiv:1904.01026

Dicke time crystals in driven-dissipative quantum many-body systems

Bihui Zhu, Jamir Marino, Norman Y. Yao, Mikhail D. Lukin, Eugene A. Demler

The Dicke model -- a paradigmatic example of superradiance in quantum optics -- describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system's dynamics are captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light-matter coupling can lead to time-crystalline-like behavior of the collective spin. In this work, we investigate whether such a Dicke time crystal is stable to perturbations that explicitly break the mean-field solvability of the conventional Dicke model. In particular, we consider the addition of short-range interactions between atoms, which breaks the collective coupling and leads to complex many-body dynamics. In this context, the interplay between periodic driving, dissipation and interactions yields a rich set of dynamical responses including long-lived and metastable Dicke time crystals, where losses can cool down the many-body heating resulting from the continuous pump of energy from the periodic drive. Specifically, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the coupling strength, suggesting the possible existence of stable dynamical order in a driven-dissipative quantum many-body system. These findings illustrate the rich nature of novel dynamical responses with many-body character in quantum optics platforms.

arXiv:1904.01039

Anomalous relaxation and the high-temperature structure factor of XXZ spin chains

Sarang Gopalakrishnan, Romain Vasseur, Brayden Ware

We compute the spin structure factor of XXZ spin chains in the Heisenberg and gapped (Ising) regimes in the high-temperature limit for nonzero magnetization, within the framework of generalized hydrodynamics including diffusive corrections. The structure factor shows a hierarchy of timescales in the gapped phase, owing to s-spin magnon bound states (`strings') of various sizes. Although short strings move ballistically, long strings move primarily diffusively as a result of their collisions with short strings. The interplay between these effects gives rise to anomalous power-law decay of the spin structure factor, with continuously varying exponents, at any fixed separation in the late-time limit. We elucidate the crossover to diffusion (in the gapped phase) and to superdiffusion (at the isotropic point) in the half-filling limit. We verify our results via extensive matrix product operator calculations.

Apr 1

arXiv:1904.00465

Superfluid Vortex Dynamics on Planar Sectors and Cones

Pietro Massignan, Alexander L. Fetter

We study the dynamics of vortices formed in a superfluid film adsorbed on the curved two-dimensional surface of a cone. To this aim, we observe that a cone can be unrolled to a sector on a plane with periodic boundary conditions on the straight sides. The sector can then be mapped conformally to the whole plane, leading to the relevant stream function. In this way, we show that a superfluid vortex on the cone precesses uniformly at fixed distance from the apex. The stream function also yields directly the interaction energy of two vortices on the cone. We then study the vortex dynamics on unbounded and bounded cones. In suitable limits, we recover the known results for dynamics on cylinders and planar annuli.